LCD dynamic backlight scaling, or dynamic luminance scaling, dynamic backlight dimming, and the like, is an efficient method to reduce LCD power consumption without hurting a user's perception. Many backlight scaling algorithms have been proposed with different trade-offs between power reduction and computational complexity.
Previous backlight scaling algorithms focus on distortion calculation and color compensation, but do not focus on histogram generation. In statistics, a histogram is a graphical representation showing a visual impression of a distribution of data. A histogram comprises tabular frequencies, shown as adjacent rectangles, erected over discrete intervals, also referred to as bins, with an area equal to the frequency of the observations in the interval. The height of a rectangle is also equal to the frequency density of the interval. Histograms are usually used to plot density of data, which is related to the size and color channel of the data.
In practice, real-time histogram generation, that is, a histogram generated at the same time when the display content updates on the display, is conducted by an application specific integrated circuit (ASIC). This approach requires an extra hardware component, the ASIC, and is not suitable for cost sensitive platforms, including smartphones and tablets. For video applications, histogram generation can be performed before the video is presented on the display in the video encoding stage with the histogram embedded as part of the video bit-stream. However, this approach does not work for many applications with display content generated by user's input, such as video games and web browsing. As a result, LCD dynamic backlight scaling is still rare in mobile systems such as smartphones and tablets. With the increase of video resolution and quality (UHD resolution and 14-bit color depth per channel), the generation of a histogram takes more computational time and power (See Table 1) and becomes more and more challenging for cost and power sensitive systems, such as mobile systems.
TABLE 1Computation time for histogram generationVideo Data720p1080pUHDUHD (14-bit)CPU692056801150ComputationmillisecondsmillisecondsmillisecondsmillisecondsTime(estimated)(estimated)of HistogramGenerationPower850118511851185 milliwattsConsumptionmilliwattsmilliwattsmilliwatts(saturated)(saturated)